The present invention relates to improvements in load sensing hydraulic brake pressure control apparatus for use in the hydraulic circuit between the master cylinder and the rear wheel brake cylinders. The apparatus is adapted for sensing variations in the distance between the vehicle chassis and the suspended axle shaft.
It is known that changes in vehicle loading cause changes in braking capability. For example, when a vehicle is fully loaded, the rear wheels will have nearly the same braking capability as the front wheels. However, when the vehicle is lightly loaded, the rear wheels may exhibit less braking capability than the front wheels. Thus the potential for premature rear wheel lock up is much greater when stopping the lightly loaded vehicle than when stopping the fully loaded vehicle. In order to compensate for the inherent imbalance between front and rear braking action, it has been customary in past years to provide a proportioning valve which restricts fluid communication to the rear wheel brake cylinders after a predetermined pressure level is generated. However, such proportioning valves represent a compromise between the desirable system characteristics for the full load condition and those for the light load condition. Thus the selected proportioning valve characteristic is neither suitable for the full load condition nor the light load condition. Many load sensing or vehicle height sensing valve mechanisms have heretofore been presented in the prior art however, they are unnecessarily complex or otherwise unsuitable for modern vehicle use. For example see U.S. Pat. Nos. 3,362,758; 3,503,657; 3,649,084; 3,684,329; 3,734,574; 3,768,876; 3,848,932; 4,150,855; 4,159,855.
The present invention relates to improvements in load responsive hydraulic brake pressure control apparatus which is placed in the hydraulic circuit upstream of the rear wheels and senses changes in the distance between the chassis and the axle of an automotive vehicle and controls the hydraulic pressure delivered from the master cylinder to the rear wheel brake cylinders in response to such changes.